The present invention relates generally to high speed digital radio frequency (RF) circuits, and more specifically to digital RF up-converters.
Wireless networks and components have been increasing in popularity at a tremendous rate over the last few years. Networking standards such as Bluetooth and IEEE 802.11 allow a wide array of devices to communicate over the airwaves, and enable connectivity at locations such as Starbucks and airports. Integrated circuits that support these and other standards continue to gain importance.
One traditional or conventional way to manufacture and design these wireless circuits is to use analog techniques. But analog circuits often require expensive external components such as tuning inductors, capacitors, and the like. Also, analog circuits often require exotic or expensive process techniques such as BiCMOS (a bipolar and CMOS combined process), SiGe (silicon substrate with germanium emitters), or other such process. Further, analog devices may require the use of devices such as Zener diodes that require additional mask steps during fabrication. These processes are more expensive than simple CMOS processes, and their use means that the analog portion cannot be integrated on a single substrate with other digital portions such as a digital signal processing circuit (DSP) or modulator-demodulator (modem). However, these analog techniques do provide operation at speeds that conventional CMOS circuits cannot achieve.
One specific circuit that has proved to be difficult to implement in a digital circuit is an RF up-converter. These circuits convert either a baseband or intermediate frequency (IF) signal to an RF signal for transmission. It would be very desirable to implement this circuit in the digital domain. A digital RF up-converter could be integrated on a large digital chip, for example an FPGA, with other digital circuits such as modems, encoders, and DSPs. Also, simple CMOS processing could be used, thus reducing manufacturing costs.
Accordingly, it is very desirable to have circuits, methods, and apparatus for implementing RF up-converters and related circuits, such as numerically controlled oscillators (NCOs), digital circuitry.